Electronic endoscope apparatus including brightness adjuster

An apparatus for adjusting the brightness of an object image, said apparatus being incorporated in an electronic endoscope apparatus, the apparatus for adjusting comprising:

• a luminance calculator that calculates a luminance level indicating a brightness of an object image, on the basis of image-pixel signals corresponding to the object image;
• a controller that calculates and outputs a manipulated value in accordance with a luminance-difference between the luminance level and a reference luminance level indicating a standard brightness of the object image, said controller setting a non-sensitive band including a standard point corresponding to the reference luminance level;
• and
• a brightness adjuster that adjusts the brightness of the object image in accordance with the manipulated value, said controller outputting a non-activating manipulated value so as not to activate said brightness adjuster when the manipulated value is inside the non-sensitive band;
• wherein the controller offsets the manipulated value so as to lower the absolute value of the manipulated value when the manipulated value is outside the non-sensitive band along a first direction that increases the brightness and a second direction that decreases the brightness by a half of a width of the non-sensitive band, the controller offsetting the manipulated value so as to maintain a linear relationship between the manipulated value and the luminance difference.

A method for adjusting a brightness of an object image that is observed by using an electronic endoscope, comprising:

• calculating a luminance level indicating a brightness of an object image on the basis of image-pixel signals, which are read from an image sensor provided in a video-scope;
• calculating a manipulated value in accordance with a luminance-difference between the luminance level and a reference luminance level indicating a standard brightness of the object image;
• setting a non-sensitive band including a standard point corresponding to the reference luminance level;
• adjusting the brightness of the object image in accordance with the manipulated value;
• and
• outputting a non-activating manipulated value so as not to activate said brightness adjuster when the manipulated value is inside the non-sensitive band;
• wherein setting the non-sensitive band comprises offsetting the manipulated value so as to lower the absolute value of the manipulated value when the manipulated value is outside the non-sensitive band along a first direction that increases the brightness and a second direction that decreases the brightness by a half of a width of the non-sensitive band, the offsetting being arranged so as to maintain a linear relationship between the manipulated value and the luminance difference.